Photographic color processing monobaths

ABSTRACT

AN AQUEOUS PHOTOGRAPHIC COLOR PROCESSING MONOBATH WHICH INCLUDES A COLOR DEVELOPER AND A FIXING AGENT, THE BATH HAVING A PH OF ABOVE ABOUT 13.2 AND BEING CAPABLE OF COLOR DEVELOPING AND FIXING AN EXPOSED PHOTOGRAPHIC FILM.

United'states Patent Oce 3,756,822 Patented Sept. 4, 1973 Int. Cl. G03c7/00 US. CI. 96-55 13 Claims ABSTRACT OF THE DISCLOSURE An aqueousphotographic color processing monobath which includes a color developerand a fixing agent, the bath having a pH of above about 13.2 and beingcapable 2f color developing and fixing an exposed photographic Thisinvention relates to photographic color processing solutions and moreparticularly relates to monobath processing solutions containing bothdeveloping and fixing agents.

In ordinary black-and-white silver halide photographic processing, aphotographic element bearing a latent image is treated with a developerto cause reduction of silver halide to visible metallic silver inlight-exposed areas of the element. Development is then arrested bytreating the photographic element with a stop solution, and thephotosensitive silver halide which remains in the element issubsequently removed by treating with a fixing solution. For reasonsassociated with processing time and expense, reduction in the number ofprocessing steps is desired, and to this end, processing baths(monobaths) capable of performing both developing and fixing functionshave been developed for black-and-white photography. Representativemonobaths are described in G. Haist, Monobath Manual, Morgan and Morgan,Inc., Hastings on Hudson, N.Y., 1966.

Silver halide color photographic processing involves development of alatent image on a silver halide photographic element by treatment with acolor developing solution employing a primary aromatic amine developer.The developer is oxidized in latent image areas of the photographicelement, and the oxidation production of the developer couples (i.e.,reacts) with a photographic color coupler compound to form a dye in suchimage areas. The metallic silver which is formed in these areas byreduction of silver halide, however, obscures the dye image and hencemust be removed. After removal from the photographic element of theremaining silver halide in a fixing bath, the metallic silver isbleached from the film by a solution capable of reoxidizing the reducedsilver to form a soluble, easily removed silver salt.

Attempts to prepare a monobath for color photographic processing whichwould permit color development, bleaching and fixing have generally beenunsuccessful. For example, H. Genda and S. Kubo, J. Soc. Sci, Phot.Japan, 21, 133 (1958) described an attempt to prepare a solution capableof developing, fixing and bleaching a color photographic element. Theresulting solution reportedly was highly unstable and caused reductionin photographic sensitivity. A monobath for photographic colorprocessing (avoiding separate development, fixing and bleaching steps)is greatly to be desired.

It is an object of the present invention to provide a stable efficientmonobath for rapid photographic color processing.

Another object of the invention is to provide a photographic colorprocessing monobath to avoid the necessity of separately removing avisible silver image.

Another object of the invention is to provide a photographic colorprocessing monobath capable of operation at elevated temperatures.

Yet another object of the invention is to provide a method for rapidphotographic color monobath processing which enables a stablephotographic color reproduction to be produced without the necessity ofperforming separate developing, bleaching and fixing steps.

Briefly, the present invention relates to an aqueous monobath for colorprocessing of silver halide photographic elements, said monobath havinga pH of above about 13.2. The monobath includes a primary aromatic aminedeveloper and a fixing agent L. The fixing agent is capable of reactingwith the silver halide in said element to form a water-soluble silvercomplex which is stable and at the pH of the monobath with the provisothat when said fixing agent is an alkali metal thiosulfate, the amountthereof is not greater than that satisfying the formula wherein pH isthe pH of the monobath, K is the dissociation constant of the silvercomplex in (moles) (liter) and [L] is the concentration of fixing agentin moles per liter.

The invention, in another embodiment, relates to a method forrapid-access color development of an exposed silver halide photographicelement which comprises treating the element in an aqueous solutionhaving a pH of at least 13.2 and which includes a primary aromatic aminephotographic developer and a fixing agent capable of reacting With thesilver halide in said element to form a water-soluble silver complexwhich is stable at said pH.

The method of the invention is preferably used with monochromatic silverhalide radiographic film, and is preferably carried out at temperaturesabove room temperature (e.g.up to about 50 C.).

The developing agents which are utilized in the present invention are ofthe primary aromatic amine type common to photographic color processing.Examples of such compounds include p-diethylamino aniline,4-diethylarnino-o-toluidine,

4- [N-ethyl-N- fi-methanesulfonamidoethyl) -aminoo-toluidine, p-N-ethyl-N-B-hydroxyethyl) -aminoaniline, and the like, which compoundsare usually provided in a stable salt form such as the hydrochloride,sesquisulfate, etc. Such developing agents are capable of reducingsilver halide to metallic silver in latent image areas of silver halidephotographic emulsion, with concurrent oxidation of the developer. Theoxidation product of the developer is capable of reacting with a colorcoupler to form a dye. The concentration of developer in the aqueousmonobaths of the invention may fluctuate widely. It has been foundconvenient, however, from the standpoint of developer solubility andrapidity of development, to employ from about 0.01 to about 0.1 mole ofdeveloper per liter of monobath.

Fixing agents utilized in monobaths of the present invention includecertain of the ordinary fixing agents known to the art. Alkali metalthiosulfates, such as sodium, potassium and ammonium thiosulfates, arepreferred, but other fixing agents, such as those of the organic thioltype (e.g., alkali metal thiocyanates, mercaptoalkanoic acids such asmercaptosuccinic acid and mercaptoacetic acid) may also be utilized.Such fixing agents complex with silver halide to form compounds whichare soluble in the aqueous monobaths of the invention, and the complexcompounds which are formed are believed to provide a ready source ofsilver ion for physical development, as will be more fully explainedbelow. The fixing agents utilized in monobaths of the invention areselected by quantity and type so that the complex produced by reactionwith silver halide is water-soluble and stable at the pH of the monobath(e.g., above about pH 13.2). The amount of fixing agent employed (fixingamount) is the amount necessary to react with the silver halide in asilver halide photographic color element in order to form solublecomplex salts therewith which can be removed readily from the emulsion,leaving the element light-insensitive. See Mees et al., The Theory ofthe Photographic Process, 3rd ed., Macmillan, New York, 1966, chap. 18.It will be understood that mixtures of fixing agents (e.g., sodiumthiosulfate and sodium thiocyanate) may be employed, and the use ofmixtures of fixing agents may be desirable to enhance the rate offixing.

Three processes are believed to occur during development of a silverhalide photographic element in a monobath of the present invention.Silver halide is reduced to metallic silver by the conventional actionof the primary aromatic amine developer, but this is a comparativelyslow reaction. Concurrently, silver halide reacts with the fixing agentto form a soluble silver halide complex which serves as a convenientsource of silver ion. Thirdly, physical development raidly occurs; i.e.,metallic silver derived from the silver ions of the soluble silverhalide complex are deposited on the latent image by electrolessdeposition. Silver which is thus deposited by physical developmentappears to be considerably less visible than is silver which is formedby conventional silver halide development, and the dye image which isformed by reaction of oxidized developer with color coupler is hencesubstantially unobscured by the formation of visible silver deposits(i.e., is transparent).

The rate of physical development in monobaths of the invention isbelieved to depend, inter alia, upon the pH of the monobath and alsoupon the concentration therein of silver ions; and the relationshipbethween physical development, silver ion concentration, and pH may beapproximated by the formula wherein f is a measure of the relative rateof physical development, K is the dissociation constant of the silvercomplex which results from reaction of the fixing agent with silverhalide (expressed in (moles) /(liter) and [L] is the concentration offixing agent in moles per liter. The variable x" represents the numberof ions derived from the fixing agent which are associated with a singlesilver ion in the complex. For an alkali metal thiosulfate fixing agent,for example, x is 2.

It will be understood that the silver ion concentration is dependent inpart upon the concentration of fixing agent in the monobtah. A greatexcess of fixing agent in the monobath will tend to depress the silverion concentration, as will too low a concentration of fixing agent. Theupper concentration of alkali metal thiosulfate fixing agents inmonobaths of the invention, for example, may be derived from the aboveequation wherein 1 must be greater than 1.0.

The pH of the bath is normally maintained at a value above about 13.2 byaddition of e.g., an alkali metal hydroxide such as sodium hydroxide.The success of the monobath of the present invention is dependent uponthe pH of the bath, which must be maintained at a value of above about13.2. Monobaths of reduced pH tend to provide images having significantvisible metallic silver. The high pH monobaths of the present inventionprovide photographic reproductions characterized by substantiallyinvisible silver deposits (thereby obviating bleaching) and furthergenerally promote efficient utilization of dye. It is further desiredthat the pH be below about 14.8, since exceedingly alkaline developingsolutions may damage colloidal binder materials (e.g., gelatin,synthetic polymers, etc.) commonly used in silver halide technology.

Best results from the standpoint of the rate of dye formation andinvisibility of the developed silver are generally obtained at a pH offrom about 13.5 to 14.2, and this pH range is accordingly preferred.

The photographic color processing monobaths of the present invention maycontain, of course, numerous other materials common to photographicprocessing solutions. For example, the monobaths of the invention mayinclude inert salts of the type ordinarily utilized to reduce theswelling of gelatin in highly alkaline solutions such as sodium sulfate;oxidation inhibitors such as sulfite-producing compounds (e.g., sodiumsulfite); Wetting aids such as sodium carboxymethyl-cellulose; colorcouplers (i.e., compounds capable of reacting with the oxidation productof primary aromatic amine developers to form dyes); fog restrainers suchas benzotriazole, potassium bromide, etc.; gelatin hardeners such asformaldehyde, glutaraldehyde and the like; organic solvents such asethylene glycol, benzyl alcohol, etc.; natural and synthetic polymerssuch as polyvinylpyrrolidone, polyvinylalcohol, etc., and auxiliarydevelopers such as hydrogen peroxide and l-phenyl- 3-pyrazolidones.

The monobaths of the present invention have been found capable ofgreatly reducing the time required for color photographic processing.For example, utilizing a color tripack film (i.e., a film containingred-, green-, and blue-sensitive layers) the total processing time canbe reduced from about 10 minutes to about 2 /2 minutes. The exposed filmneed only be treated in a monobath of the invention to cause developmentof a colored image and fixation of unreduced silver halide, and washedto remove the processing chemicals from the film.

In a preferred embodiment, monobaths of the invention are utilized todevelop and fix monochromatic (couplercontaining) radiographic film toprovide a radiographic record having a colored image. The eye isapparently able to detect more readily small differences in imageintensity in radiographic films containing color images than inconventional radiographic films. In another embodiments, the monobath ofthe invention may contain one or more color couplers capable of forminge.g., blue dyes. Radiographic film (preferably lightly tinted yellow)may be developed in this monobath to yield a radiographic reproductionhaving a bluish image upon a yellow background. The present inventionthus provides a very valuable method for rapid processing ofradiographic films to provide color radiographic reproductions.

Generally it has been found desirable to employ the monobath of thepresent invention at temperatures exceeding 23 C. Althoughroom-temperature processing yields good results, elevated temperatureshave been found to advantageously increase the rate of development andfixation without diminishing the quality of the dye image, therebyfurther reducing processing time. Bath temperatures of up to 47 C. andabove can be employed, although temperatures from about 30 C. to about40 C. are preferred since this range contributes to rapid processing andyet avoids the problems associated with photographic processing athigher temperatures (gelatin degradation, excessive fog, etc.).

The invention may be more clearly understood by reference to thefollowing illustrative examples wherein the densities referred to aredye densities.

EXAMPLEI A solution of:

G. p- ('N-ethyl-N-thhydroxyethyl)amino aniline (as sulfate salt) 4Sodium sulfite 10 Sodium sulfate 60 Sodium thiocyanate 1 Potassiumbromide 2.9 Sodium thiosulfate 19 Water to 800 ml.

TABLE I (NaOH) g./

800 m1. pH 7 mnx EXAMPLE 2 An image-wise exposed photographic elementbearing on a transparent support a silver iodobromide radiographicemulsion containing1-hydroxy-2-N-(n-octadecylcarbonamido)naphthalene-4-sulfonic acid cyanforming coupler was processed for 7 min. at ambient temperature in abath of the following composition p(N-ethyl-N-fl-hydroxyethyl)aminoaniline (as the sulfate) 4 Potassiumbromide 2.9 Sodium sulfite 10 Sodium sulfate 60 Sodium hydroxide 18.4Sodium thiosulfate 13 Water to 800 ml.

Bath pH 13.6.

After washing with water, analysis of the imaged element showed a D of0.16, a D of 2.30, and a 'y of 1.0. The cyan image was transparent.

EXAMPLE 3 To 200 ml. of a stock solution of 2-methyl 4 [N-ethyl N(B-sulfonamidoethyh] aminoaniline (as sesquisulfate) 16 Sodium sulfiteSodium sulfate a 50 Potassium bromide 0.6 Sodium thiocyanate 1 Sodiumhydroxide 3 Water to 800 m].

To another 200 m1. portion of the stock solution of Example 3 was added2 g. sodium hydroxide and 5 g. sodium thiosulfate to yield a pH of 13.5.A sample of the film described in Example 3 was processed therein for 2min. at room temperature and then washed. Thereafter, 0.1 g. of1-phenyl-3-pyrazolidone was added as an auxiliary developer to the 200ml. of monobath, and another sample of film was identically processedtherein and washed. The following table lists the photographic results:

TABLE 11 Speed) Dmlu Din" 7 (re].)

Control with 1-pl1enyl-3-pyrazolidone. EXAMPLE 5 The following colordeveloping solution was prepared:

2-methyl-4-[N-ethyl N (B sulfonamidoethyD] aminoaniline (assesquisulfate) g 16 Sodium sulfite g 5 Sodium sulfate g 50 Potassiumbromide g 0.6 Sodium thiocyanate g 1 Sodium hydroxide g 19 Ethyleneglycol ml 25 1-(2,4,6-trichlorophenyl)-3-(4-nitroanilino) 2pyrazoline-S-one (magenta-forming coupler) g.. 1.7

Water to 800 ml.

A sample of the photographic element of Example 3 was exposed through asensitornetric wedge and was developed in the bath for 2 min. at roomtemperature. After development, processing was completed according toconventional procedures (bleaching, fixing). The developer was thenconverted to a monobath of the invention by addition of 13 g. of sodiumthiosulfate. Another film sample was processed in this monobath for 6min. at ambient temperature, and washed. The following results were Asilver halide color tripack film was prepared by coating consecutivelyonto a subbed triacetate film base.

(a) A magenta-forming silver chlorobromide emulsion sensitized to greenlight and containing1-(2,4,6-trichlorophenyl)-3-(N'-p-dodecylphenylureido) 2 pyrazoline5-one.

(b) A magenta-forming silver iodobromide emulsion naturally sensitive toblue light and containing N'-(abenzoylacetyl) p aminophenylsulfon (0'cyclohexylanilide, and

(c) A cyan-forming silver chlorobromide emulsion sensitized to red lightand containing (1-hydroxy-4-chloro- N-tetradecyl-2-naphthamide.

Each coating contained 10 milligrams of silver per square decimeter.

The resulting film was exposed to light through color separation filtersin a sensitometer and thereafter was treated for three minutes at 21 C.in a monobath hav- Water to 1 liter.

After washing and drying, the following results were obtained:

Water to 200 ml.

A photographic element having coated on a transparent film base agelatino silver iodobromide emulsion containing an oil-dispersedcyan-forming coupler (1-hydroxy-4- chloro-N-tetradecyl-Z-napthamide) wasdivided into three parts which were respectively processed in the bathat 23 C., 35 C. and 47 C., followed by washing in 1% aqueousformaldehyde solution. The following photographic data were obtained:

8 EXAMPLE 9 A silver chlorobromide emulsion containing an excess of adibutylphthalatetriphenylphosphate dispersed cyanforming coupler(l-hydroxy-4-chloro N tetradecyl-Z- naphthamide) was dispersed ingelatin and coated on a subbed polyester base. The resultingphotographic element was divided into sections, and each section wasexposed to 190 meter-candle-seconds of illumination and was thenprocessed for 3 minutes at ambient temperature in a monobath of thefollowing composition, the pH of the monobath being varied by additionof sodium hydroxide as given in Table VII below.

p-(N-ethyl N 9 hydroxyethyl)-amino aniline (as the sulfate) Sodiumsulfite 10 Sodium sulfate 60 Potassium bromide 2.9 Benzotriazole 1Sodium thiosulate (1) Water to 1 liter.

1 See Table VII.

Table VII gives the resulting dye densities as a function of thiosulfateconcentration, and further gives the value of fin the equation TABLE vwherein pH is the pH of the solution, K is the dissocia- ReL Processingtion constant (3.5 Xl0 of the silver halide complex e n rature,C. Dmin.Dim. 7 speed time of 25 C. in (molesY /(liter) and [L] is the concentra-23 0,1 82 0 5 6 1 mm non of fixing agent U1 moles per liter. 0.08 0.860.5 2.7 30sec. 47 0.00 1.50 0 0 5.8 30sec. 35 TABLE v11 Sodiumthiosultate,gramslliter pH f D EXAMPLE 8 14.2 3.2 Coating failed Aphotographic element bearing, on a subbed polyester 14- 2 2 33 5 toclear. base, a silver iodobromide emulsion to which had been 1 m 1 addedan excess amount of an oil-dispersion of the yellowforming couplerN'-(a-benzoylacetyl)-p-aminophenylsul- 14,2 jfon-(o-cyclohexyloxy)-anilide was prepared and was out 3 23 imageintofour sections, each of which was then exposed to 30 13.2 1122 0I7Imeter-candle-seconds of illumination through a continu- Nolmageouswedge. One section was processed at room temperature for 4 minutes in amonobath of the following composition:

Sodium thiosulfate 49 Sodium sulfate 60 Sodium sulfitc 10 Potassiumbromide 3 Sodium thiocyanate 1 Sodium hydroxide 92 p-(N-ethyl N 18hydroxyethyl)-amino aniline (as the sulfate) Water to 800 ml.

TABLE VI D (above fog-monsured through Wratten #47 filter) Additionaldeveloping agent added I claim:

1. An aqueous color processing monobath for color processing of silverhalide photographic elements, said monobath having a pH of at least 13.2and including a primary aromatic amine color developer and a fixingagent L capable of reacting with said silver halide in said element toform a water-soluble silver complex which is stable at said pH with theproviso that when said fixing agent is an alkali metal thiosulfate, theamount thereof is not greater than that satisfying the formula pH +1og1.0

wherein pH is the pH of said monobath, K is the dissociation constant ofsaid silver complex in (moles) (liter) and [L] is the concentration offixing agent in moles/ liter.

2. The monobath of claim 1 wherein the pH of said monobath is from about13.5 to about 14.2.

3. The monobath of claim 1 which additionally includes a photographiccolor coupler.

4. The monobath of claim 1 wherein said fixing agent is sodiumthiosulfate.

5. The monobath of claim 1 wherein said fixing agent is amercaptoalkanoic acid.

6. An aqueous photographic color processing monobath of pH 13.2-14.8comprising (a) a primary aromatic amine developer; and

(b) sodium thiosulfate in an amount not greater than that satisfying theformula pH+log (%).0

wherein pH is the pH of said monobath, K is the dissociation constant ofthe silver complex resulting from the reaction between silver halide andsaid sodium thiosulfate in (molesV/(liter) and [L] is the concentrationof fixing agent in moles/liter.

7. A method of developing and fixing a color silver halide photographicelement which comprises treating said element in the monobath of claim1.

8. A method of developing and fixing a color silver halide photographicelement which comprises treating said element in the monobath of claim3.

9. A silver halide photographic element bearing a color image producedby the method of claim 7.

10. A method for rapid color processing of an exposed photographicsilver halide element which comprises developing and fixing said elementin a single color processing monobath of pH 13.2 to 14.8 and whichincludes a primary aromatic amine developing agent and a fixing agentcapable of reacting with silver halide in said element to form awater-soluble silver complex stable at said pH, and washing saiddeveloped and fixed element.

11. The method of claim 10 wherein said fixing agent is sodiumthiosulfate.

12. The method of claim 10 wherein said developing and fixing isaccomplished at a temperature of from above 23 C. to about 50 C.

13. A method for rapid color processing of an exposed photographicsilver halide element which comprises developing and fixing said elementat a temperature of from 40 C. in a color processing monobath of pH 13.2to 14.8 and which includes a primary aromatic amine developing agent andan alkali metal thiosulfate, and washing said developed and fixedelement.

References Cited UNITED STATES PATENTS 2,626,215 1/ 1953 Schwerin 96-61M 2,857,274 10/1958 Land et al. 96-61 M 3,512,980 5/ 1970 Lucas 96-61 M3,615,509 10/1971 Klein 96-61 M 3,255,008 6/1966 Tefft 96-61 M NORMAN G.TORCHIN, Primary Examiner R. L. SCHILLING, Assistant Examiner US. Cl.X.R. 96-61

